The present invention relates to hydraulic anti-skid braking systems for vehicles of the kind in which the vehicle brakes are pulsed or pumped to reduce the possibility of wheel lock-up. The latest and probably most valuable invention in the automotive market today is the introduction of the anti-lock braking system. It is by far the most important safety feature in automobiles today and may be mandatory in the cars of tomorrow as the safety belt today is. The systems installed in today's cars are the more complex versions, where sensors are installed in each wheel to detect the occurrence of a skid or incipient skid or lock-up condition. In one example of the prior art, information that sensors gather causes a high pressure hydraulic pump to reduce the pressure in the wheel that is just about ready to skid. In this manner, the wheels are allowed, in a controlled fashion, to be relieved of pressure from the brake shoe or pad in order to rotate again, albeit in a very short period of time. As soon as the wheels start to rotate, the computer again tells the hydraulic pump to apply pressure to the brakes in order to stop the wheels from rotating. This sequence is repeated normally 4 times/second. It is known that the maximum braking action is achieved just before the wheels skid on a surface. In view of the level of complexity of the devices now being offered in the marketplace of which applicant is aware, these "off-the-shelf" devices are not readily retrofitable on vehicles purchased without one from the factory. This device being applied for in this application will achieve the same effect as the computer controlled one but will perform anti-skid control in a more economical and retrofitable manner.
The instant invention differs from the prior art in that the instant system avoids the complexities of the valving arrangements of the prior art. The simplification is accomplished by reducing the number of parts of the system and by relying upon an improved piston for performing the critical functions. The instant system is easily retrofitable to existing automobiles equipped with the conventional tandem hydraulic cylinder.